This invention relates to spark ignition direct injection (SIDI) engines and to a method of operating a split engine having two cylinder groups with separately throttled intake air systems.
It is known in the art relating to spark ignition direct injection engines to operate an engine in a stratified charge mode in a lower range of engine output and in a homogeneous mode in a higher range of engine power output with an intermediate zone wherein the cylinders operate in a combination of stratified charge and homogeneous charge combustion.
It is also known to operate homogeneous charge engines in a split manner wherein one group or bank of cylinders may be deactivated while the other group or bank is operated nearer unthrottled operation in order to provide improved engine efficiency in the lower power ranges. At higher power ranges, the deactivated cylinder group or bank is again powered in order to supply additional power for increased output operation of the engine. Split engines may be controlled by a throttle to cut off air flow to one of the cylinder groups or banks or by cutting off fuel flow to the deactivated cylinders or a combination wherein both air and fuel are cut off to the deactivated cylinders.
The present invention provides a modified form of operation for a spark ignition direct injection (SIDI) engine having separate intake air passages to two cylinder groups which are controlled by individually actuated throttles, preferably of the electronically controlled type. The cylinders of both groups are capable of operation in a stratified charge mode in a lower range of cylinder output and a homogeneous mode in a higher range of cylinder output with a small crossover range in between wherein both stratified and homogeneous charge operation may be conducted. The cylinder groups preferably have an equal number of cylinders arranged for alternate firing of cylinders from each group. Any cylinder arrangement, such as inline, V-type and opposed, can be utilized.
In a preferred embodiment as applied to a V-type engine, the cylinders are equally divided between two cylinder banks, preferably arranged for alternate firing of the cylinders from one bank to the other. Intake air flow is divided into separate throttle controlled passages which feed separate intake manifolds one connected to each of the cylinder banks to supply separately controlled air charges to the cylinders of the separate banks. Conventional direct injection (DI) fuel injectors are provided for each of the cylinders for injecting fuel directly into the cylinders.
In the stratified charge mode the fuel is injected during the piston compression stroke, preferably into a piston bowl from which it is directed to a spark plug for ignition near the end of the compression stroke. In the homogeneous charge mode, fuel is injected directly into each cylinder during its intake stroke and is allowed to mix with the air charge entering the cylinder to form a homogeneous charge which is conventionally ignited near the end of the compression stroke.
In the stratified charge mode the cylinders are primarily operated unthrottled, except possibly at the lower or idle end of their power range, and the engine power is controlled by the amount of fuel injected into the cylinders during each engine cycle. In the homogeneous charge mode, the fuel injected by the injectors is controlled as a function of the air admitted to the cylinders by the separately controlled throttles so that an ignitable homogeneous charge is provided, and power is controlled by the mass of air inducted and fuel injected into the cylinders. Except for the use of the split air intake, the forgoing represents the conventional method of operating an SIDI engine.
In accordance with the invention, an improved method is provided for operating an SIDI engine having two groups of cylinders supplied with air by separate manifolds each controlled by a separate throttle.
In a lower range of engine power output, both groups of cylinders are operated in a stratified charge mode with essentially unthrottled intake of air into the cylinders, together with varying the mass of fuel delivered to the cylinders to control the engine power output.
In a higher range of engine output, both groups of cylinders are operated in a homogeneous charge mode wherein the air to the cylinders is throttled as required to control the engine output between an intermediate and a maximum power range. In this mode, both cylinder groups or banks may be operated at the same power level or, alternatively, one cylinder bank may be run unthrottled while the other cylinder bank is throttled to control the total power of the engine output.
In an intermediate range of engine power output between the lower and higher ranges, one cylinder group is operated in a homogeneous charge mode near maximum output with unthrottled or only slightly throttled intake air, as required. The other cylinder group is operated in a stratified charge mode with essentially unthrottled intake air. In this mode, power is controlled by varying the mass of fuel delivered to the cylinders of the group operated in the stratified charge mode to control the engine power output.
If desired, control of throttling may be further accomplished by supplying exhaust gas recirculation to the cylinders in order to reduce the amount of throttling required and further increase the efficiency of the engine operated in accordance with the improved method.